NOISSUE refactor pack import (extraction and paths)

It now:
* Doesn't extract until it knows the content format is good.
* Extracts in a predictable location, not requiring to use a second path for the actual pack root.

api/logic/BaseInstanceProvider.h

@@ -37,7 +37,7 @@ public:
 	{
 		return QString();
 	}
-	virtual bool commitStagedInstance(const QString & keyPath, const QString & path, const QString& instanceName, const QString & groupName)
+	virtual bool commitStagedInstance(const QString & path, const QString& instanceName, const QString & groupName)
 	{
 		return false;
 	}